Totally possible, and some teams do. You need a state store, a evaluator job, a propagation layer to push state changes to every instance, a SDK, a dashboard, alerting, audit logging, RBAC, and a fallback strategy for when the coordination layer itself goes down.

It's not complex individually, but it takes time, and it's the ongoing maintenance that gets you. Openfuse is a bet that most teams would rather pay $99/mo than maintain that.

That said, a self-hosted option is on the near-term roadmap for teams that need it.